One of the first things you want to do when the temp drops outside is turn up the heat inside. However, before you touch that furnace make sure your furnace is ready to be touched.
Remove any boxes or other items you may have stored close to it during the summer months. Also, make sure you change your filter frequently.
Call your public service company (many people in Colorado are not serviced by Xcel) or a certified tech if you have questions about where your detector should be located.